Musannaf Ibn Abi Shayba 13:672

Abu Bakr narrated to us, he said: Isma'il bin 'Ayyash narrated to us, from 'Abd al-'Aziz bin 'Ubayd Allah, from 'Amir, from Ibn Mas'ud, he said: The offspring of the *mudabbara* (a slave woman promised freedom upon her master's death) are in the same status as her. They are emancipated by her emancipation, and they remain in slavery by her remaining in slavery.